1. Field of the Invention
The present invention relates to a semiconductor integrated device comprising a reference voltage generating circuit and a circuit that generates high-frequency noise.
2. Description of the Related Art
There are many semiconductor integrated devices which contain a reference voltage generating circuit for the purpose of causing stable operation of the internal circuits, reducing power consumption and the like, and in which a reference voltage is supplied to the internal circuits from this reference voltage generating circuit. Furthermore, semiconductor integrated devices also exist which have external terminals that output the reference voltage of the reference voltage generating circuit to the outside. In such cases, a capacitor which has a large capacitance is connected to the external terminals in order to absorb high-frequency noise which is difficult for such a reference voltage generating circuit to absorb. Generally, in such a reference voltage generating circuit, the operational amplifier and the like, which are constituent elements of this circuit, react to low-speed signals; accordingly, low-frequency noise can be well absorbed.
The construction of the reference voltage generating circuit and surrounding parts in such a semiconductor integrated device is shown in FIG. 3. The semiconductor integrated device 101 contains a semiconductor chip 102, leads 111 and 112 whose end portions on the opposite ends from the ends facing the semiconductor chip 102 constitute external terminals, and bonding wires 121 and 122 which connect these leads 111 and 112 with the semiconductor chip 102. The semiconductor chip 102 contains a reference voltage generating circuit 141, an analog circuit 142, a digital circuit 143, and bonding pads 131 and 132. Furthermore, the reference voltage generating circuit 141 is electrically connected to analog circuit 142, digital circuit 143 and bonding pad 131, and the analog circuit 142 is electrically connected to bonding pad 132, respectively by metal wiring formed on the surface of the semiconductor chip 102. Moreover, the bonding pad 131 is electrically connected to the end portion of the lead 111 facing the semiconductor chip 102, and the bonding pad 132 is electrically connected to the end portion of the lead 112 facing the semiconductor chip 102, respectively by the bonding wires 121 and 122. An externally attached capacitor 110 which is used to absorb high-frequency noise is connected to the lead 111.
Accordingly, the output of the reference voltage generating circuit 141 is supplied to the analog circuit 142 and digital circuit 143; furthermore, this output is supplied to the lead 111 via the bonding pad 131 and bonding wire 121. Input-output of the analog circuit 142 is accomplished by means of the lead 112 via the bonding pad 132 and bonding wire 122.
As a result, in cases where high-frequency noise is generated in the digital circuit 143, it may be expected that this noise will be absorbed by the externally attached capacitor 110 via the bonding pad 131, bonding wire 121 and lead 111.
The abovementioned description also similarly holds true in cases where the digital circuit 143 is replaced by an analog circuit that is different from the analog circuit 142 and that generates high-frequency noise. Depending on the type of analog circuit used, there may be circuits in which noise (including high frequencies) is generated, and there may be cases in which such circuits are mounted on semiconductor chips along with analog circuits that are vulnerable to noise.